1. Field of the Invention
The present invention relates to polyimide films, and more particularly to polyimide films having a low dielectric constant.
2. Description of the Related Art
Electronic products require increasingly thinner, smaller and lightweight printed circuit boards (PCB). Moreover, because wireless internet and communication devices operate at higher frequency, efforts have been made to develop circuit boards capable of high transmission rates. Basic requirements for the materials of the circuit boards include the ability to transfer data at a high rate, and prevent data alteration or interference during transmission.
It is known that the transmission speed in semiconductor devices is mainly limited by the occurrence of delay between metal wires carrying the signals. In order to reduce the delay in signal transmission, an insulating layer having a low dielectric constant is usually arranged between the wires, which can reduce capacitance coupling between the wires, enhance the operation speed and reduce noise interference. The insulating layer can block the flow of an electric current, and a lower dielectric constant can reduce the occurrence of undesirable stray capacitance. Moreover, the insulating material should have a dissipation factor that is as small as possible to minimize waste of electric energy.
Owing to its good thermal resistance, good chemical resistance, high mechanical strength, and high electrical resistance, polyimide has been widely used in electronics industry, for example, as material for making a printed circuit board. However, the dielectric constant and the dissipation factor of the conventional polyimide films may still be undesirably high for high-frequency applications. Furthermore, certain applications may require the use of a polyimide cover film having a low transmittance to cover and conceal the circuit design to prevent illegal copy. Usually, low gloss is also required for the polyimide cover film to provide better appearance.
Accordingly, there is a need for a polyimide film that can address the aforementioned issues and have desirable film characteristics.